a notch on (someone's) belt

A remarkable success or achievement, especially one in a successive string, list, or tally of other such ones. (Can also be formulated as "a notch on the belt of someone.") The successful negotiation of the merger between the two companies was another notch on the young executive's belt. It wasn't a particularly difficult match, but the win is nevertheless a notch on the belt of the defending champion. You sold your first million-dollar house? Well, there's a notch on your belt as a realtor!